Antenna configurations for compact device wireless communication

ABSTRACT

A diversity antenna for use with a portable host device such as a laptop computer, for example as part of a PCMCIA card pluggable into the laptop computer to enable wireless computer by the laptop computer, includes a main antenna and a diversity antenna. Various configurations for these antennas are possible, including the use of a balanced dipole as the main antenna element and a split diversity antenna for the diversity antenna element. The diversity antenna provides high isolation between the antenna elements and isolation from interfering self-noise generated by the host device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 60/967,449, filed on Sep. 4, 2007, entitled “AntennaSystems”, the disclosure of which is hereby incorporated by referencefor all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to antennas for use with portable and othercomputing devices, such as laptop computers. More specifically, itrelates to antennas that may be part of removable components such asPCMCIA (personal computer memory card international association) cardsor the like that provide wireless communication to the computingdevices.

2. Description of the Related Art

Some computing devices, such as laptop computers, may not bemanufactured with wireless communication capability. Rather, some ofthese devices may have slots or similar coupling locations into whichwireless communication devices may be mated to provide the hostcomputing device with wireless capability. The wireless communicationdevice can be for example a PCMCIA (personal computer memory cardinternational association) card, and can include a transceiver and othercircuitry coupled to an antenna and matable with the host device toprovide wireless communication capability thereto. While explainedherein in terms of a laptop computer as the host device, and a PCMCIAcard as the wireless communication device, it will be appreciated thatthe invention is not so limited, and other host devices, such as PDAsand desktop computers, and other wireless communication devices forestablishing wireless communication through a cellular network orthrough Bluetooth, WiFi and other types of wireless links and channelsare also contemplated.

Diversity antennas used with wireless communication devices, especiallyportable and mobile devices, are very beneficial in improving thequality of the received signal in a wireless communications receiver.Typical diversity antenna systems consist of a main antenna and adiversity antenna, although there could be more than one diversityantenna. The initial benefit of diversity comes from the de-correlationof the fading between two separate antenna systems. The antennas can bespatially separated and/or use orthogonal polarizations (i.e. verticaland horizontal polarizations, right and left circular polarization,etc.) During a fade, the signal strength is degraded to the point thatlong error bursts occur in the received signal, severely degrading theoverall received radio throughput, amongst other degradations. Diversityhelps alleviate this problem by having two antennas separated in spaceand/or polarization, providing two nearly independent receive signalchannels or paths which do not experience fades in the same way (thatis, they are de-correlated). Thus while one antenna may experience adeep fade the other antenna may be within 3 dB of its nominal signallevel. The result of this is that links with rapid fading that can go−15 dB or more below the average signal strength in a fade on a singlechannel system (non-diversity) but may be reduced to only −4 dB or −5 dBbelow the average signal strength with diversity on a statistical basis.In this example, diversity would provide an effective gain of 11 dB to10 dB. Thus the reduced loss of signal prevents the channel from beingdropped far less frequently than it would with a single deep fadingchannel. Typically the diversity antenna may be separated by as littleas one eighth of a wavelength and still experience a significant gainover a single channel non-diversity antenna.

FIG. 1 a shows a simple two antenna diversity system used on a PCMCIA(personal computer memory card international association) card 10 in alaptop computer 12, in which two vertical dipoles or monopoles (11 and13) are employed. In FIG. 1 b, an orthogonal dipole/monopoleconfiguration is shown that uses a vertical monopole/dipole 14 withhorizontal monopole 15 disposed normal to the side of the laptop case.In FIG. 1 c, the horizontal monopole is replaced with a PIFA (PlanarInverted-F Antenna) style antenna 17 and a vertical antenna 16. Both thePIFA and the horizontal monopole use the laptop case as the“counterpoise” for the associated antenna system. An “antennacounterpoise” is a virtual ground for balancing the currents in theantenna by establishing a zero reference potential for feeding theactive antenna element. It can be any structure closely associated with(or act as) the ground which is connected to the terminal of the signalreceiver or source opposing the active antenna terminal, (that is, thesignal receiver or source is interposed between the active antenna andthis structure). The “antenna counterpoise” may be directly,capacitively or inductively coupled to the surrounding ground plane ifthere happens to be one there.

One of the main disadvantages of these sample diversity systems is thegenerally poor isolation between the antennas, sometimes as low as a fewdB but typically only 6 dB. With diversity isolations greater that 10 dBbeing preferred, consideration may be given to improved orthogonalitybetween these antennas to increase the diversity isolation. Higherdiversity isolation essentially means less correlation between theseparate antennas and therefore a reduced probability of destructiveinterference or fading.

Another consideration is the interactions between a dipole like-antennaand an orthogonal dipole/monopole with a substantially symmetricalgeometry normal to the main dipole length vector. Small form factorwireless communications devices, such as PCMCIA cards, provide verylimited external space to include antennas with high efficiency, widebandwidth, multiple bands and diversity all at the same time. This tightspace constraint results in interaction between the various antennaelements, even if the antennas have good isolation between the selectedpaths or “ports.” This is further complicated by the interaction betweenthe various antenna systems and the computer or platform to which thecard is mated.

Thus one consideration is the fabrication of a high performance main anddiversity antenna system for use in a PCMCIA card, with the aim ofachieving good antenna efficiency with high isolation between the mainand diversity antennas and high isolation between the main antenna andthe radiated self-noise from the host device (for example lap topcomputer), while maintaining an acceptable industrial design (ID)appearance. These results are ultimately reflected in the TotalIsotropic Sensitivity (TIS) and Total Radiated Power (TRP) performanceof the antenna.

Optimum dipole location for minimum laptop self-noise is anotherconsideration. Laptop computers have traditionally been designedprimarily for user computer functionality and conformity with FCC part15 regulations. In more recent times, functionality has been expanded toinclude wireless network connections such as cellular communications andWiFi. Since the FCC part 15 requires only radiated noise limitations,the issue of self-noise for added or integrated wireless networksolutions has not been considered. Consequently, while compliance withFCC part 15 has been achieved, there are high levels of RF surfacecurrents and RF voltage antinodes all over laptop computers.Furthermore, laptop computers now can have prescribed locations at whichPCMCIA cards and similar devices can be added after-market, and theselocations have become the location for accommodating wireless solutions.The concern is that self-RF noise generated or reaching in theselocations de-senses the receiver part of the transceiver. Radiation inthe PCMCIA slot regions may be substantially vertically polarized, andconduction currents from the laptop chassis generate conduction noiseinto antenna structures, such as the traditional monopole, that use thechassis as the substantial counterpoise for the antenna. This lattercase can be the main mode of self-noise for PCMCIA-based wirelessmodems. The lowest noise is generated in the region of the PCMCIA slotin the E-field direction parallel to the long edge of the slot openingin the laptop.

FIGS. 12 a-12 c show a typical laptop computer with a PCMCIA or other PCcard slot 1201 in the side wall of the laptop 1200. The electric fieldsEx, Ey and Ez are shown as indicated. FIGS. 12 b and 12 c showconventional antenna configurations as currently employed. The extensionof the PCMCIA card 1206, 1206′ outside of the slot is shown. In FIG. 2b, the antenna 1207 is in the form of a typical monopole antenna thatuses the laptop chassis as its counterpoise, and the antenna 1208 is inthe form of a vertical antenna that can be a monopole that uses thechassis as its counterpoise, or the antenna could be made longer andconfigured as an end-fed dipole that is only weakly coupled into thechassis. Antenna 1209 is in the form of a PIFA (Planar Inverted-FAntenna). This style of antenna excites currents and voltage antinodesin the associated ground plane, which acts as a counterpoise to thePIFA. Put simply, the PIFA is a wide monopole that excites the groundplane.

With the exception of the end-fed dipole antenna, all of the antennas ofFIG. 12 a-12 c suffer from conducted RF noise from the chassis or groundplane of the computer. The end-fed dipole operates best when excited ata low impedance point on the ground plane or chassis. Since this dipoleantenna is end-fed, it represents a very high impedance to the groundplane and hence reduces the conducted noise to the dipole.

Optimum dipole location and shape for maximum bandwidth in a smallvolume is another consideration. Almost all laptop computers today haveat least one slot available for mating a PCMCIA card or similar deviceto the laptop computer. The extent of the projection of a PCMCIA cardoutside the slot in the side of the laptop is primarily limited byaggressively small industrial design (ID) constraints that have littleconcern for the needs of RF antenna functionality. Additionalconstraints are imposed by the mechanical enclosure and its requirementsfor welding line wall thickness and studs and so forth.

The size of an antenna enclosure has the greatest influence on theantenna performance at the lowest required operating frequency. For anideal fat dipole the optimum length is 0.45λ, with λ being thewavelength of the interest. However, for cell-phone applications,adequate performance can be achieved with top-loaded dipoles or fatdipoles with a length as short as 0.30λ. Antennas as short as 0.125λrequire significant top-loading and often require sophisticated matchingcircuits to achieve the necessary bandwidth.

In addition, the location of a dipole antenna near a significant groundplane also impacts the bandwidth and performance of a dipole antenna. Byway of example, a Yagi antenna requires a minimum separation ofreflector from the driven element (typically a dipole) of 0.04λ. Theoptimum separation is 0.15λ to 0.25λ with adequate performance as closeas 0.09λ. As the separation decreases below 0.25λ, the front to backratio decreases to unity and the bandwidth also decreases.

By way of example, Novatel™, in the C110 Type II PCMCIA card, uses aYagi style antenna with the ground plane of the PCMCIA card as thereflector, a balun-fed dipole, and a director in order to operate above1.90 GHz in a cellular application. The spacing between elements isnominally at the minimum of 0.04λ as a result of needing to fit withinan overall length of 22 mm. This antenna is integral with the main PCB(printed circuit board) and requires no external antenna components. Thefolded nature of the antenna elements reflect the struggle to achieve amatch even at this high frequency, let alone attempting a solution at0.824 GHz. The very nature of this three-element Yagi design renders a0.824 GHz solution extremely inefficient and/or limited bandwidth.

Optimum dipole location and style for minimum specific absorption rate(SAR) in a small volume is yet another consideration. SAR is a directmeasure of the amount of RF power absorbed into human tissue due to atransmitting device in close proximity to it. This is a particularlyimportant mobile phone issue as the transceivers of the device areemployed in close proximity to the operator's head. The requiredstandards and conditions for the measurement of SAR are defined andregulated by the FCC. There are several basic approaches to SARreduction:

-   -   1. Reduce the radiated RF power    -   2. Place a screen between the radiator and the tissue    -   3. Place a resonant reflector between the radiator and the        tissue    -   4. Use an antenna design with a significant front-to-back ratio,        pointing the null towards the tissue.    -   5. Increase the separation distance between the radiator and the        tissue    -   6. Spread out the surface current more over the radiator,        particularly close to the radiator feed point in the case of a        dipole or a monopole.

While these seem like simple remedies they each come with a cost, and atrade-off is required that usually impacts either industrial design (ID)and/or antenna and system performance.

Most traditional PCMCIA or PC cards are designed with a single PCB inmind, with antenna assemblies added to the outside edge of the card. Theantenna elements typically comprise monopole antennas, whip antennas orPIFA (planar inverted-F antenna) antennas. Some use a coplanar dipole asthe radiator, but this has been the choice of expedience of parts and ofhaving a minimum vertical profile. This latter application, if used atall, has mostly been used at 1.8 GHz and above, due the unacceptablesize of the antenna at lower frequencies such as 850 MHz.

The SAR “hot spot” most typically occurs close to, if not directlyunder, the feed point for the antenna. FIG. 15 a shows a normal monopole1501 used in a PCMCIA card 1520 in a laptop computer 1500. The antennafeed point 1502 is at the intersection point between the laptop 1500case and the monopole 1501. Directly below this point and in the nearsurface of the tissue of the operator is where the “hot spot” 1503 willusually be found. The same result occurs for a whip antenna, whethernormal or vertical at the feed point. The use of a standard dipole 1504is shown in FIG. 15 b, with its associated SAR “hot spot” at 1505beneath the dipole. In some cases a Yagi antenna can be used in lieu ofthe dipole, to achieve some SAR reduction.

Inductive coupling between the antenna assembly and the printed circuitboard (PCB) is another consideration. In some situations, it may bedesirable to use such inductive coupling. An inductive couplingarrangement can be useful with air core transformers having only a fewturns on both primary and secondary sides, for instance. However, suchair-cored transformers have significantly more flux leakage than a highMu ferrite-cored transformer. This flux leakage constitutes theuncoupled magnetic flux that does not pass through both coils. Theconsequence of this leakage is to produce an uncoupled inductance calledleakage inductance. This acts in series with both the primary andsecondary sides of the transformer, whereas the common inductance iscalled the mutual inductance and accounts for the magnetic field that isaccepted by both sides of the transformer. While the leakage inductanceis often perceived as loss, it is in fact conservative and can becancelled out by using series capacitance or shunt capacitance. The mainissue is that if the leakage (uncoupled) inductance exceeds the mutualinductance, the capacitive tuning required will result in a narrowerband coupling.

The simplest design rule to minimize the flux leakage is to widen thetrace width and to push the two windings as close together as possible.Once the gap-to-width ratio drops below 0.2, the leakage inductancebecomes much less that the mutual inductance.

An advantage of the use of inductive coupling is that it simplifies theinterconnection between two RF circuits, which, in the case of anantenna assembly, is between the PCB containing the bulk of thecircuitry and the FPCB (flexible printed circuit board) of the antennaelement(s). The inductive coupling eliminates the need for directsoldering, coaxial connection, zif sockets or pogo pins, etc. Theperceived disadvantage is the leakage inductance and the size of thecoupling loops, which is directly related to the maximum operatingwavelength.

Reference is first made to FIG. 16 a, in which conventional arrangementin which a balun 1601 on a main PCB 1630 is used to drive the antenna(not shown) or other balanced device in a differential manner. Balun1601 is connected directly to a balanced antenna feed system 1603 via agap port 1602. This interconnect is typically soldered, RF connected,pogo pinned, zif connected or facilitated by some other mechanicaldevice or means (not shown). Next, in FIG. 16 b, there is shown aconventional arrangement in which the connection of a dipole 1606 is viaa feed line 1605 to a balun 1604. The balun is disposed on PCB 1630′.The gap exists at the balun-to-feed system transition. This gap can becoupled to the RF system by micro-strip or strip-line across the gap.The balun 1604 is made large enough to establish an adequate amount ofinductive reactance so that the system does not become too low inimpedance.

Dual band gap split duplexer and/or matching is also a consideration.Balanced RF feed systems are often a consequence of symmetrical RFmodules such as antennas, mixers, differential/push pull amplifiers,coplanar waveguides and other such devices. Solutions as describedherein are applicable to all these areas, even thought the principlefocus is for antenna applications and balun structures includinginductive/transformer coupling.

With reference to FIGS. 17 a-17 e, conventional gap port feed systemsare described. In FIG. 17 a, it is gap 1702 across a balun 1701; in FIG.17 b, it is in a notch 1704 of a notch antenna 1703; and in FIG. 17 c itis across the central region of a closed end slot 1706 of a notchantenna 1705.

The gap port defines the excitation region of the selected balanced RFsystem. The gap port is the subject of the transition from the balancedto the unbalanced RF circuit that needs to be connected to theantenna/balun. It should be understood that the edge opposite to the gapon the balun may be connected to a large or larger ground plane on whichthe RF circuits reside and still maintain the balanced/symmetricalcondition. The balance remains as long as the attached ground plane isattached symmetrically to the balun even if it connects to the twoadjacent sides as well.

FIG. 17 d is an isometric view showing how a slot (or gap) 1708 in aground plane is typically connected into a strip line 1709 feed systemin an antenna system 1707. In the system 1707, the strip line 1709connects to the opposite side of the gap/slot from where the line camefrom. In the side view of FIG. 17 e, it is seen where the slot 1708 iscoupled in a short circuit to the strip line 1709 at a point 1713opposite on the slot. A similar configuration is shown in FIG. 17 f, butin this case the strip line 1709′ passes across the slot 1708′ andbeyond it by a distance of one quarter of a wavelength, ending in anopen circuit. This well-practiced principle in strip line RF designshown in FIG. 17 f effectively achieves a short circuit as in thelocation 1713 in FIG. 17 e without the necessity of a direct electricalconnection. This methodology finds its greatest use for the excitationof slot or notch antennas and also for the excitation of patch on slotantennas.

BRIEF SUMMARY

Described herein is a dual diversity antenna system with orthogonaldipole and monopole elements designed to have a substantiallysymmetrical pattern, high efficiency, high isolation between thediversity elements, and reduced sensitivity to nearby sources ofelectromagnetic interference.

As described herein, a diversity antenna system for use with a hostdevice and configured to provide isolation from radiated self-noise bythe host device and to minimize interactions between antenna elements ofthe diversity antenna system. The diversity antenna system includes aground plane, a main antenna coupled to the ground plane and having acommon mode feed, and a diversity antenna having first and second armsextending from the common-mode feed of the main antenna.

Also described herein is a diversity antenna system for use with a hostdevice and configured to provide isolation from radiated self-noise bythe host device and to minimize interactions between antenna elements ofthe diversity antenna system. The diversity antenna system includes aground plane, a main antenna including a first portion of the groundplane and a first notch formed in the first portion, and a diversityantenna including a pair of balanced notches formed is a second portionof the ground plane.

Also described herein is a diversity antenna system for use with a hostdevice and configured to provide isolation from radiated self-noise bythe host device and to minimize interactions between antenna elements ofthe diversity antenna system. The diversity antenna system includes aground plane, a main antenna, a diversity antenna orthogonal to the mainantenna, and a double balun configured to provide independent feeds tothe main and diversity antennas.

Also described herein is a diversity antenna system for use with a hostdevice having a ground plane, the diversity antenna system beingconfigured to provide isolation from radiated self-noise by the hostdevice and to minimize interactions between antenna elements of thediversity antenna system. The diversity antenna system includes a mainantenna, a diversity antenna orthogonal to the main antenna, a firstbalun coupled to the main antenna, and a jumper configured as a secondbalun for exciting a common mode of the main antenna.

Also described herein is a diversity antenna system for use with a hostdevice having a ground plane and a case, the diversity antenna systembeing configured to provide isolation from radiated self-noise by thehost device and to minimize interactions between antenna elements of thediversity antenna system. The diversity antenna system includes a mainantenna coupled to the ground plane, a balun having a gap and coupled tothe main antenna, a common mode feed for the main antenna, the commonmode feed configured to excite the gap of the balun, and a diversityantenna having first and second arms extending from the common modefeed, the diversity antenna being configured to use the case as acounterpoise.

Also described herein is a diversity antenna system for use with a hostdevice and configured to provide isolation from radiated self-noise bythe host device and to minimize interactions between antenna elements ofthe diversity antenna system. The diversity antenna system includes aground plane, a main antenna coupled to the ground plane and comprisinga dual-band symmetrical center fed dipole, and a diversity antennacoupled to the ground plane and configured to operate as a top loadedmonopole.

Also described herein is a diversity antenna system for use in awireless transmission device removably pluggable into a host device,with the diversity antenna including a ground plane, a main antennacoupled to the ground plane and having at least one portion that isconfigured to be elevated relative to a surface of the wirelesstransmission device that is closest to a user of the system such thatSAR (Specific Absorption Rate) to the user is minimized, and a diversityantenna coupled to the ground plane and configured to operate as a toploaded monopole.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings:

FIGS. 1 a-1 c are schematic views of various known diversity antennaconfigurations.

FIGS. 2 a-2 c show three sets of balanced symmetrical antenna systemsthat are orthogonal.

FIGS. 3 a-3 d show various diversity antenna configurations.

FIG. 4 a shows a high isolation diversity antenna.

FIG. 4 b is a schematic diagram depicting the magnetic potential flow ofthe antenna system of FIG. 4 a.

FIG. 4 c is another view of the diversity antenna of FIG. 3 a, showingin addition the polarization directions involved.

FIGS. 5 a and 5 b show two configurations of split diversity antennas.

FIG. 6 a is a schematic diagram showing the use of a power splitter.

FIG. 6 b is a schematic diagram illustrating a circuit equivalent of aWilkinson power splitter.

FIG. 6 c is a schematic diagram showing a splitter with odd modematching that provides optimum matching for a dual band application.

FIGS. 7 a-7 b show a PCMCIA card including a diversity antenna.

FIGS. 8 a-8 b show the details of an antenna assembly for use in thePCMCIA card of FIGS. 7 a-7 b or the like.

FIGS. 9 a-9 b show further details of an antenna assembly for use in thePCMCIA card of FIGS. 7 a-7 b or the like.

FIGS. 10 a-10 b show details of an inductive coupling scheme.

FIGS. 11 a-11 b show details of an antenna assembly including details ofthe diversity antenna and circuit components associated therewith.

FIGS. 12 a-12 c show a laptop compute and various prior art antennaconfigurations for use therewith.

FIGS. 12 d-12 f are isometric views relating to optimum antennaplacement in a PC card mated to a laptop computer.

FIGS. 13 a-13 c and 14 a-14 d are isometric views relating to optimumdipole antenna placement in a PC card mated to a laptop computer.

FIGS. 15 a-15 b are isometric views showing hotspot locations for pccards in use in a laptop computers to which they are mated.

FIGS. 15 c-15 e show pc cards in which portions of the antenna assemblyand/or pc card housing are raised to reduce hotspots.

FIGS. 16 a-15 b show conventional balun type feeds.

FIGS. 16 c-16 l show various inductive coupling configurations.

FIGS. 17 a-17 f show various prior art feed configurations for gapantennas.

FIGS. 18 a-18 c relate to various feed configurations for a duplexantenna application.

FIGS. 19 a-19 b relate to various matching configurations possible forthe duplex antenna application.

FIGS. 20 a-20 h show various matching elements that can be used.

FIG. 21 shows a duplexer antenna with a balun feed.

FIG. 22 is a prior art block diagram of a pc card or the like.

DETAILED DESCRIPTION

The description herein is provided in the context of antennaconfigurations for compact device wireless communication. Whileexplained in terms of a laptop computer as a host device, and a PCMCIAor similar PC card as the wireless communication device, it will beappreciated that the invention is not so limited, and other hostdevices, such as PDAs and desktop computers, and other wirelesscommunication devices for establishing wireless communication through acellular network or through Bluetooth™, WiFi™ and other types ofwireless links and channels are also contemplated. Moreover, theprinciples of the invention are not restricted to communication devicesthat are designed to mate with host devices to provide wirelesscapability thereto, but are more generally applicable to cellulartelephones, two-way radios, and other self-contained wirelesscommunication devices that may be equipped with their own antennas orantenna systems.

Those of ordinary skill in the art will realize that the followingdetailed description is illustrative only and is not intended to be inany way limiting. Other embodiments will readily suggest themselves tosuch skilled persons having the benefit of this disclosure. Referencewill now be made in detail to implementations as illustrated in theaccompanying drawings. The same reference indicators will be usedthroughout the drawings and the following detailed description to referto the same or like parts.

In the interest of clarity, not all of the routine features of theimplementations described herein are shown and described. It will, ofcourse, be appreciated that in the development of any such actualimplementation, numerous implementation-specific decisions must be madein order to achieve the developer's specific goals, such as compliancewith application- and business-related constraints, and that thesespecific goals will vary from one implementation to another and from onedeveloper to another. Moreover, it will be appreciated that such adevelopment effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skill in the art having the benefit of this disclosure.

With reference to FIG. 22, a block diagram of a wireless communicationdevice 200 such as a PCMCIA card or other PC card is shown. As explainedherein, wireless communication device 2200 can be mated with a hostdevice, such as a laptop computer or the like, to provide wirelesscommunication capability thereto. The basic components of wirelesscommunication device 2200, whose functions are well known and do notwarrant a detailed explanation here, include a modem circuit 2201, aradio control circuit 2203 and a transceiver circuit 2205. Generally,radio control circuit 2203 can be in the form of a processor or the likeand serves functions such as control of various components and theirinteractions, decoding of speech signals, and so on. The transceivercircuit 2205 may serve functions such as a multiplexing/demultiplexingsignals to and from antenna system 2207. Modem circuit 2201 may beresponsible for functions such as coding/decoding of data andtransmitting same to or from the host device. Also included in wirelesscommunication device 2200 is an antenna or antenna system 2207, whosefunction is to receive and/or transmit wireless signals over one orseveral RF frequency bands. The antenna system 2207 can have any ofmultitude configurations, depending on the application, as detailedbelow.

In the case of a diversity antenna system using two antennas, improvedorthogonality between the diversity antennas can be achieved by usingtwo orthogonal symmetrical and/or balanced antennas. FIGS. 2 a-2 c showthree sets of balanced symmetrical antenna systems that are orthogonal.These are antenna system 21 comprising a balanced dipole with a toploaded normal monopole (FIG. 2 a), antenna system 23 comprising abalanced dipole with differential and common mode feeds (FIG. 2 b), andantenna system 25 comprising dual orthogonal notched antennas (FIG. 2c). In the first two cases (21 and 23), the main antenna is a balanceddipole 24 excited through a symmetrical balun 26. A balun(balance-unbalance) is a device designed to convert between balanced andunbalanced electrical signals, such as between coaxial cable and ladderline. Baluns can be considered as simple forms of transmission linetransformers. In the third case (25), a symmetrical and balanced notchantenna 30 is used as the main antenna. In all three cases the mainantenna extends in a direction parallel to the top face 18 and parallelto the side face 19 of the laptop host device 27 from which the PCMCIA(personal computer memory card international association) card extends.

It will be appreciated that in antenna systems the division of areceiving structure into “antenna” and “feeder” is to some extentarbitrary. Typically, the feeder conveys received power from thestructure to the receiver component. If this is performed by means of atransmission line, possibly twin balanced feeder lines or coaxial cable,or by means of waveguide, the metal of the feeder structure must passthrough the near field region of the antenna proper, thus modifying theantenna currents and hence the properties of the otherwise isolatedantenna. In a balanced antenna receiving structure formed from dipolesor collections of dipoles, the instantaneous voltages on the two arms ofthe dipole can be resolved into two types of modes, differential (odd)and common (even) with respect to the dipole center of symmetry and toobjects at large distances. The radiation properties of the antennaelements when fed in common mode will be quite different from those whenfed in differential mode. If such an antenna is fed from an unbalancedfeeder (coaxial cable, for instance) then there will be a mixture ofthese modes excited depending on how the feed is connected to theantenna structure. Objects in the near field of the antenna, which donot preserve the symmetry of the antenna structure, may also unbalancethe antenna and give rise to coupling between the odd and even modes andwill therefore distort the antenna pattern and balance.

An important example of the effects of unbalance in radiating systemsmay be seen in the PC card form factor wireless device plugged into alaptop computer platform, which typically consists of a metal framesurrounded by a plastic shell. In this situation, the laptop computerplatform takes the place of a ground plane to a large extent. Theantenna is therefore primarily a monopole in relation to this “groundplane”. However, there will be currents flowing on the laptop computersurfaces (in particular, the metallic surfaces inside the laptop), whichwill contribute to the radiation properties. There is usually onlycapacitive coupling from the antenna(s) of the wireless device antennato the laptop, and indeed, the laptop may be placed on an insulatingdielectric surface (wood table for example), in which case the antennaelements may be balanced by the equivalent length of the case containingconducting material. In this case the radiating structure looks morelike a dipole. In a typical antenna installation, the receiving elementis a balanced dipole. Very often the feed is an “unbalanced” coaxialcable; reflections at the feed-dipole junction will give rise tocurrents flowing along the outside of the coaxial cable braid. Thiscontributes to the radiation, and the polarization sensitivity may bealtered from the orientation of the dipole elements. It also affects theradiation pattern and the positions of the nulls. The problem can beaddressed with the provision of a balun (balance to unbalancetransformer).

Returning to FIGS. 2 a-2 c, the diversity antenna 31 consisting ofelements 32 and 34 shown in FIG. 2 a is center fed from the ground planedirectly below using the common mode feed 36. Since this top loadeddiversity antenna 31 is common mode fed, the currents flow down the twoarms (32 and 34) in an opposite sense in the direction horizontal andparallel to the computer case. This results in zero effective currentflowing in this direction due to the feed used. Thus there can be nocoupling between the main dipole antenna 24 and the common mode feedpoint 36 so long as the symmetry is maintained. There is, however a netcurrent flowing in the two arms 32 and 34 in the direction normal to thecomputer laptop case. This current does flow into the common mode feedsystem 36 and uses the computer case as its counterpoise. The result isa top loaded monopole normal to the computer case face at this point. Itshould be noted that there will be coupling between the main antenna 24and the odd mode in the diversity antenna top loading that is parallelto the computer case. As will be described below, this may be used toenhance the antenna performance in the main antenna, although it canalso be a source of significant loss.

A “mode” on an antenna describes the electric current and potentialdistribution on the antenna conductors. Modes are decomposed intoorthogonal even and odd symmetry. An even mode will have an even integernumber of effective half wavelengths including 0. An odd mode will havean odd integer number of half wavelengths. Typically in a center feddipole antenna, the current will flow in the same direction in the feedline at the feed point for an even mode and in the opposite directionfor an odd mode.

In FIG. 2 b, the second diversity antenna 38 uses the common mode of themain antenna 24 and a double balun 40 connected to the ground plane toachieve a non-balanced dipole. This dipole is orthogonal to the maindipole and therefore achieves high isolation.

The last example of FIG. 2 c—antenna system 25 comprising dualorthogonal notched antennas—shows two balanced notches 41, 42 cut intothe notch ground plane 44. These two notches can be combined using a gapfeed and a Wilkinson power splitter combiner or similar device tocombine the notch signals in phase and thereby produce an effectivehorizontal dipole normal to the computer case face. Such a system willbe highly isolated from the main antenna 30. In FIG. 2 c, it can be seenthat Nd1 and Nd2 combine to reject Nm and to enhance response in the Eydirection.

FIGS. 3 a-3 d show further details of the diversity options and someadditional options as well. FIG. 3 a is a more detailed view of antennasystem 21 comprising a balanced dipole with a top loaded normal monopoleas in FIG. 2 a. The diversity antenna 31 is fed from port 33 and usesthe computer case 35 as its counterpoise. The main feed 37 excites thegap of balun 26 that is connected to the balanced dipole antenna 24.FIG. 3 b shows an antenna system 23 comprising a balanced dipole withdifferential common feeds as In FIG. 2 b, but in greater detail. Notethe two independent feed systems 46 and 48 for the main and diversityantennas, respectively. FIG. 3 c shows an antenna system 23′ using abridged version for the balanced balun of FIG. 3 b. The main feed systemtravels along the balun 50 through the center portion of the dual feedsystem 52 to the main feed line 54. A metal jumper 56 connects the dualfeed system 52 to the diversity antenna feed 58. FIG. 3 d is an antennasystem 23″ which is a simplified version of antenna system 23′ ofarrangement C and uses a jumper 56′ as a balun to excite the common modeof antenna 24 with the ground plane connected to the computer case. Themain 62 and diversity 64 feeds are also shown in this sketch. A furthervariation can be realized if the arrangements of FIGS. 3 b, 3 c and 3 dare designed such that the common mode of the main dipole acts as thecounterpoise for the diversity antenna when the stem to the left becomesthe other side to this second dipole. This stem may be isolated througha “feed style trap” from the case of the main module or modem. This trapwould be a coaxial or stripline or equivalent feed that uses the outsidesurface as an RF trap either as a distributed quarter wavelength shuntor shortened using capacitive loading on a shorter length shunt (hairpinstyle trap). This would still maintain symmetry with the main dipole,thus allowing for excellent cross-polarization isolation. Additionallythis second dipole (in place of the diversity monopole) could be madesymmetrical and balanced with respect to itself as well by adding twoarms symmetrical with the common mode arms of the main dipole. If thereis sufficient clearance below the two dipoles, the two dipoles can befully crossed in an orthogonal manner, allowing for perfect symmetry inboth horizontal axes. In this latter case the new system could berotated by any angle in the horizontal to best fit the availablegeometry. One such rotation would be 45 degrees. Clearly, twosymmetrically crossed dipoles do not require the other for counterpoisepurposes.

As previously explained, antenna system 21 comprising a balanced dipolewith a top loaded normal monopole of arrangement of FIG. 3 a is fed fromport 33 and can use the computer case as its counterpoise. The main feed37 excites the gap of balun 26 that is connected to the balanced dipoleantenna 24. An alternative realization of such a high isolationdiversity antenna system 66 is described with reference to FIGS. 4 a-4c. In FIG. 4 a, the effective ground plane 68 of the PCMCIA card case(fabricated from metal) and the computer case 70 are also shown. Themain antenna shares components 24, 26 and 37 with the main antenna ofantenna system 21. The diversity antenna 71 includes L-shaped arms 72and 74. Although shaped differently from diversity antenna 31 of antennasystem 21, diversity antenna 71 is essentially functionally the same.The common mode feed system is port 76.

FIG. 4 b shows the magnetic potential flow of the antenna system 66,associated with the current flow, at both the main and diversityantennas. The magnetic potentials 78, 80 show the same direction andtherefore will mutually couple in the direction of the magneticpotential 80. The effective magnetic potentials 82, 84 cancel out, butreinforce in the direction normal to the magnetic potential 80. The main86 and diversity 88 feed systems connect to the RF circuit (not shown)located in and on the ground plane 68. The isolation for thisarrangement has been found to be better than 30 dB. With improvedsymmetry, it may be possible to improve this isolation even further,although already it is more than sufficient for the intendedapplication.

It will be appreciated that FIGS. 4 a and 4 b relate to a top-loadedmonopole (71) style of antenna, but it should be noted that it is a veryuseful improvement to split the monopole and in particular the toploading section into a left and right section about the axis of symmetryinto two distinct components that can be separately fed in phase andcombined through a power combiner. This separation gap may besignificant but typically not exceeding one tenth of a wavelength inmost cases. A discussion of such an arrangement appears below.

Another aspect relates to the use of a high isolation diversity antennawith an orthogonal main balanced dipole. As previously explained, forthe antenna systems 21 and 66, there are two basic “high isolationantennas” each consisting of a main antenna (24) and a diversity antenna(31, 71). The main antenna 24 is the same in both cases and uses a balunfeed to excite the dipole. The diversity antennas 31 and 71 are fed inthe common mode with ports 33 and 76, respectively. With reference toFIG. 4 c, it is shown that orthogonality results from the orthogonalpolarization E_(m) of the main antenna 24 being orthogonal to the commonmode of the diversity antenna 31,71 having a polarization E_(c). Thisarrangement is basically a monopole that uses the effective ground planeof the computer case and the ground plane of the PCMCIA card as itscounterpoise. For reference purpose the feeds 37′ and 33′ for the main(24) and diversity (31) antennas, respectively, are also shown.

The excitation of the odd mode in the top loading of the diversityantennas 31,71 due to the main antenna 24 should also be considered.While this odd mode does not couple into the common mode (also known asthe even mode) of the diversity antenna, it does mutually couple withthe main dipole antenna. This is the case with other forms of antennassuch as a slot, notch or patch antennas. The result of the mutualcoupling is a modification of the impedance of the main antenna, andthis may have either a beneficial or deleterious effect on the matchand/or bandwidth, depending on the circumstances.

The odd mode excitation can be modified by breaking the diversityantennas at their center, creating finite gaps 90, 92, between separatearms 94, 96 and 98, 100, as seen in FIGS. 5 a and 5 b. The gaps can befrom small to substantial in reference to a quarter of a wavelength.Regardless if the symmetry is maintained, so will the isolation bemaintained. With the diversity antenna thus open circuited, there can beno odd mode excitation Ed due to the main dipole antenna 24. However,the simple cut also defeats the common mode excitation. The remedy is touse a wide band in-phase Wilkinson style power splitter 102, shown inFIG. 6 a, to drive the split arms 94, 96 and 98, 100 via Feed-A andFeed-B. The Wilkinson power splitter 102 splits the input signal intotwo equal-phase output signals. Such a device will produce, at itsoutput, the common/even mode of the diversity antenna, while isolatingthe odd mode by providing high isolation between the two arms in thedifferential, or odd, mode. Alternatively or additionally, a matchingcircuit can be used across the gap to promote the match and bandwidth ofthe main dipole antenna whilst still maintaining the high isolation. Avery simple reduction of a Wilkinson splitter, designated 104 in FIG. 6b, can also be realized using discrete components as shown. This networkis useful in narrow band applications; however, it will be appreciatedthat more complex splitters, distributed and discrete, can be usedprovide for wide bandwidths.

In cases where the odd mode coupling has a negative effect on the mainantenna, the splitter method can correct this. However, it is oftenpossible to use the mutual odd mode coupling in a way that providesimproved broad banding of the main antenna. As seen in FIG. 6 a, amatching section 106 has been added between the Feed-A and Feed-B. Inthis case the matching section 106, so long as it maintains a highimpedance in the common mode to ground, does not change the common modematch at the output. Thus a network can be designed either discrete,distributed or both that optimizes the reactance in the odd mode thatachieves maximum bandwidth due to the mutual coupling.

A schematic for the above diversity/main antenna system is shown in FIG.6 c using a splitter 108 with odd mode matching that provides optimummatching for a dual band application operating in two bands over oneoctave apart in center frequency. The best main antenna bandwidth may beachieved for the high band when the resonator is slightly capacitive inreactance and the inductor 110 in combination with the dominantcapacitance of the series resonator 112 at the low band produced thedesired optimum performance in the main antenna when the combination(110, 112) was of high impedance in the low band. Clearly the choice ofthe match is a function of the ground plane, the location of thediversity antenna, and the location of the main antenna and the targetedband. Other configurations are possible and can be tuned using modelingtools and/or a vector network analyzer. In an application in the band1.9 GHz, the usable bandwidth was almost doubled by the proper selectionof components, including the selection of a low inductance feed line inthe two arms 94, 96 and 98, 100 of the diversity antenna.

Previous PCMCIA card products have demonstrated poor isolation betweenthe main antenna and the diversity antenna and also poor isolation ofthe main antenna from unwanted noise generated in the host lap topcomputer which are well known for high radiated self noise particularlyas processor speeds are increasing and contaminating the wirelessspectrum in the proximity of the slots for PCMCIA cards. This is furtherimpacted by the lack of tight RF shielding in typical laptops where therequirement is to meet FCC part 15 requirements and little attention isgiven to self noise issues outside of these FCC limits. An external scanof a typical laptop will show maximum radiated noise in the verticalpolarization with respect to the keyboard plane and also in anyconducted path between the antenna and the laptop case. The most quietzone for a dipole is easily observed when the antenna length axis isparallel to the side of the laptop.

Typically whip antennas and PIFA antennas, that are notoriouslyunbalanced, have been used in the past for the main and diversityapplications with generally troublesome results in performance and, inparticular, isolation, due mostly to the conducted noise mentionedabove.

To address these and other problems, use can be made of a symmetricalbalanced dipole parallel to the host computer face containing the PCMCIAcard slots, an orthogonal diversity antenna with optimized mutual oddmode coupling, inductive coupling to simplify and cost reduce mainantenna connection to the main ground plane, and a centrally andsymmetrically located upward pointing RF switch connector. The limiteddipole length particularly impacts the lowest frequency band, in thiscase the cellular band. Top loading of the low band element of thedipole brings the antenna back to resonance and provides for improvedbandwidth. The high band—namely the PCS band—is already of ideal lengthso the same extent of top loading is not required and a bowtie dipolecan be implemented.

To reduce SAR (specific absorption rate), the dipole can be raised atits center in the vertical direction since the SAR is relatedsubstantially to the magnetic field generated by the RF current maximumat the dipole center. SAR is a measure of the amount of radio frequencyenergy (radiation) absorbed by the body when using a radio transmitterdevice such as a cell phone, PCMCIA card, and the like. Increasingdistance will reduce the SAR in accordance with the inverse square law.In addition, the dipole width can be maximized, which furtherdistributes the current, causing the magnetic field to spread further,thereby significantly reducing SAR. Further, since the current is low inthe top loaded region of the low band dipole, this can be folded downtowards the ground where there is likely SAR impacted tissue withoutincreasing SAR yet allowing decreased dipole resonance and bandwidth ina compact volume.

FIG. 7 a shows a PCMCIA card 120 having a card connector 122, a case 124and an antenna section 126 having a dielectric cover. FIG. 7 b is a viewshowing the antenna assembly 127 with the dielectric cover removed fromthe antenna section 126. An RF connector 128 disposed centrally andoriented in an upward direction can be seen, along with a flexibleantenna FPCB (flexible printed circuit board) 130 having an antennasupport shown generally at 132 for supporting the FPCB. FPCB 130 isfolded to assume a substantially three-dimensional shape for theantenna.

FIGS. 8 a-8 b show the details of the antenna assembly 127. A mainantenna ground plane 136 connects to the card ground plane 134 includingthe case and, in turn, this connects to the host ground plane throughthe PCMCIA interface connector 122 (FIG. 7 a). The FPCB antenna 130 isshown supported by the plastic antenna carrier or support 138, which ispart of the antenna support 132 (FIG. 7 b). The wings 142, 144 of thetop loaded diversity antenna 140 are disposed on the main PCB (PrintedCircuit Board) 146 and connect to the diversity feed system (not shown)behind the main RF connector 128. An inductive coupling mechanism 150,described in more detail below, couples the main antenna FPCB 130 tobalun loop 148 formed in the ground plane 134. This connection providesfor a connector-less, solder-less coupling between the main antenna andthe balun 148.

As seen from FIGS. 9 a and 9 b, the main antenna FPCB 130 includes ahigh band bowtie-style dipole antenna 152 having wings 154, 156 and alow band top-loaded dipole antenna 153 including portions 158 a-b, 160a-b. Respective feed arms 158 c, 160 c are provided for low bandtop-loaded dipole antenna 153. A main antenna feed 162 is also provided,as is an inductive coupling loop 164 disposed on the underside of PCB146. Of particular note is the alignment of the dipole length axesrelative to the host computer/laptop, and in particular, in parallelrelation to the side of the laptop case into which the PCMICA card isinserted. Of further note is the deliberate height or elevation of thecentral part of at least one of, and in this case both, the dipoles 152,153, so configured to minimize SAR. The elevation is of the central partof the dipoles is relative to the bottom of the card 120 (FIG. 7 a),which bottom may be closest to the user when the PCMCIA card is pluggedinto the laptop the laptop is placed on the user's lap. The elevationthus increases the distance from the user and reduces SAR to the user.

Low band tuning (of antenna 153) is achieved by adjusting the tabs 158a, 160 a. The tuning of the high band bow-tie antenna 152 is determinedby the notches 165 in the pattern near the feed 162. Thus FPCB 130operates as a dual-band symmetrical center fed dipole fed from aninductively coupled loop balun. The main RF connector 128 is also shownwith the diversity antenna 140 located behind it.

FIGS. 10 a and 10 b show more detail of the coupling mechanism 150,which includes coupling loop 164 for FPCB main antenna 130 inconfronting relationship with main ground plane balun loop 148. Mainground plane balun loop 148 can be printed on both sides of the main PCBthus providing for strip line coupling to the gap in the main loop. Thestripline then connects to the matching circuit 166, shown in FIGS. 11 aand 11 b, on the main PCB. If the loop is only on a single side of themain PCB then a microstrip coupling is used. This in turn connects withthe matching circuit 166.

FIGS. 11 a and 11 b show more details of the diversity antenna 140,which has feeds 168 and 170 for arms 142, 144, respectively. The widthof the feeds 168, 170 determines the series inductance of the diversityantenna and has a significant impact on the main antenna match in thePCS high band. A power divider and odd mode matching section is showngenerally as the cluster of components 170 comprising a shunt capacitor172, two series inductors 174, 176 joined to the common mode feed systemat node 178. The ground plane 136 for the main antenna system is shownwith the balun coupling loop 148 and matching components 166 for themain antenna match. These matching components are connected to the loopcoupling gap by either stripline or microstrip line.

It is possible to effect some modifications to the main antenna FPCBfeed arms, making them wider in order to allow for lower SpecificAbsorption Rate (SAR) due to the spreading of the radiating power over alarger FPCB area, particularly in the feed arm region.

The consideration of optimum dipole location for minimum laptopself-noise is discussed with reference to FIGS. 12 d-12 f. The optimumpolarization for the PCMCIA card antenna in a laptop has been found tobe in a direction parallel to the long edge of the slot opening 1202 andE field Ex illustrated in FIG. 12 d. In particular, position 1203depicted in FIG. 12 d provides an improvement in noise rejection by atleast 10 dB in all bands. This is due to the polarization and thebalance of the antenna. Therefore, to couple to the least noise from thelaptop chassis, one solution is to use a balanced antenna with itspolarization in the Ex direction 1203.

There are several candidate antennas that will provide this solution.The first, seen in FIG. 12 d, is a dipole 1210 that is center-fed.Antenna 1210 is kept balanced with a balun feed system 1211; however, itwill be appreciated that any differential feed system can be used. Thesecond candidate is the antenna in 1212 in FIG. 12 e. Antenna 1212 is anotch antenna that may be fed across the notch at a location that bestserves the desired matching impedance. In a sense this is also a type ofbalun-feed, as in FIG. 12 d. Modifications to the notch can be used toprovide traps and other such devices to lower the center frequency andto improve the bandwidth and match of this antenna. In principle, thenotch and balun-fed dipole antenna can morph into one another asnecessary.

The third candidate is a slot antenna 1213, shown in FIG. 12 f. Thisantenna can also be modified as necessary to improve bandwidth match andlower center frequency without departure from the spirit and scope ofthe invention. An important advantage of this configuration isminimization of laptop-generated noise coupling into the antennastructure.

The consideration of optimum dipole location and shape for maximumbandwidth in a small volume is explained with reference to FIGS. 13 a-13c and 14 a-14 b. With short dipoles (often referred to as Hertziandipoles), the current distribution from the center of the dipole to thetip decreases linearly to zero. This results in a very short regionwhere the radiation-inducing current is effective. With a standarddipole, the roll-off is a cosine form, which results in a much widerregion over which the radiation-inducing current is effective, togetherwith the fact that the antenna is longer anyway. This radiation currentis the substantial generator of the far-field magnetic field component.For a dipole, the longer the radiation current region is, the higher theeffective radiation impedance will be. As it turns out, this radiationcurrent region will be reduced as a reflector approaches the antennastarting at 0.25λ, thus ultimately shorting out the antenna at zerodistance, with λ being the wavelength of the interest. It is thereforeimportant to locate the radiation current region as close as possible to0.25λ from a reflector for the best results. While the use of one ormore directors in the front of the dipole would help the back-to-frontratio, this also impacts the overall length of the antenna and thereforewould most likely violate the industrial design constraints.

FIGS. 13 a-13 c respectively show three balanced dipole or dipole-likeantennas. The first antenna 1301 in FIG. 13 a is a basic balun-feddipole located within a controlled length enclosure of length Lid asmeasured from the side face of the laptop computer to the end of thewireless communication device, in this example a PCMCIA card pluggedinto the laptop computer. The dipole effective radiation current Ix is adistance La from the reflector face 1305 (that is, the side edge of thelaptop case, which behaves as a reflector). For best performance, thisdistance La should be in the range of about 0.15λ<La<0.25λ, although adistance as short as about 0.09λ could work.

The diagrams in FIGS. 13 b and 13 c show a notch antenna 1307 and atop-loaded dipole antenna 1311, respectively. The effective radiationcurrent Ix distances from the ground plane reflector are depicted as Lnand Lc, respectively. The top loading 1309 of the dipole antenna 1311allows the effective current Ix to be more spread out than a shortdipole would allow.

FIGS. 14 a-14 c relate to three configurations (1413, 1415 and 1417) ofa top-loaded dipole in a PCMCIA card arrangement. The respectiveeffective Ix distances of the dipoles from the reflector face 1305 inthese configurations are Lc, Lcr and Lcf. Clearly Lcf offers thegreatest separation between the radiating current region and the laptopcase/reflector, and still falls within the maximum industrial designlength of Lid. Moreover, the longer the distance Lcf, the easier it isto achieve the required lowest frequency specification and, furthermore,as this length increases, so will the antenna bandwidth.

FIG. 14 d shows a more detailed version of a top-loaded dipole 1420 thatincludes the dipole arm 1421, a meander choke/inductor 1422, andtop-loading scheme 1423. The top-loading is folded over as shown tomaximize the length Wda of the dipole arms 1421. Maximizing this lengthin particular increases antenna bandwidth. Similarly, widening thedipole arm thickness Lda in the Ey direction also increases antennabandwidth.

For the lowest operating frequency with an aggressive industrial designlength, the top-loaded dipole design 1417 (FIG. 14 c) offers the optimumconfiguration for the best bandwidth and efficiency performance for adipole antenna in a PCMCIA card application in a laptop computer. Thisdipole arm provides the greatest antenna current flows, which can be atthe maximum distance away—up to about 0.25λ. Furthermore, in theinterest of maximum antenna bandwidth, the antenna arm depth should alsobe maximized, even to 0.25λ also, although lesser depths are oftensatisfactory.

In situations where additional operating bands are required, these willbe clearly at higher frequencies and can therefore be included insidethe lowest band top-loaded dipole which will be furthest to the front.These additional dipoles may not require top-loading and may also sharea common feed system. There may be a requirement to include sometrap/high inductance elements between the front dipole 1419 and itsassociated top-loading section to minimize loading of the higherfrequency dipoles.

The consideration of optimum dipole location and style for minimumspecific absorption rate (SAR) in a small volume, for example incellular telephone, or a PC card such as a PCMCIA card, is discussedwith reference to FIGS. 15 c-15 e. The separation distance between thehotspot and the tissue of the operator is the most effective SAR remedy.The SAR decreases with approximately the inverse square of theseparation distance. Hence, doubling the distance will reduce the SAR bya factor of 4. In the disclosed antenna system it has been recognizedthat primarily the high-current portion of the antenna needs to beraised to reduce SAR. Similarly, broadening and lengthening the highcurrent portion also reduces the SAR significantly, particularly if theantenna is thin in the region of the feed point.

In the SAR mitigation configuration described with reference to FIGS. 15c-15 e, a PCMCIA card is shown plugged into the laptop computer 1500. InFIG. 15 c, the dipole antenna 1506 of PCMCIA card 1520″ is shown to beraised above the feed plane 1513. This rise is labeled Hdc as measuredfrom the lower surface of the card enclosure or housing. The SAR “hotspot” 1508 is decreased as the height Hdc is increased. In actuality,only the high current region starting from the feed point and includingthe dipole arms needs to be raised, as beyond this point the SAR istypically much lower and hence the need for separation distance is lesscritical. In view of this, the dipole ends can be lowered to anappropriately satisfactory industrial design (ID). Such a design isdepicted in FIG. 15 d, in which the arms 1509 are raised, while thedipole ends 1511 are folded back down as shown. The feed plane islabeled 1513′ and the hotspot is labeled 1508′ in FIG. 15 d. The topsurface of the enclosure may be raised accordingly to accommodate theraised portions of the antenna, as shown. Furthermore, the location intowhich the PC card is mated in the side face of the laptop computer 1500may be raised by a distance Hct to further separate the hotspot from theuser during use, as when the laptop and PC card are resting on the usersthighs.

The use of a top-loaded dipole also allows the overall antenna dipolearm length to be reduced, with that length being taken up by the dipoleends. However, reducing the arm length may cause the SAR to increase asthe current becomes more concentrated near the feed point, so acompromise must be made. In the side view of FIG. 15 e, the top-loadingportion 1517 of the dipole is shown, with a meander line choke orinductor 1516 connecting to the dipole arm 1509′ appearing in end view.This choke or inductor 1516 allows the antenna to be resonant at a lowerfrequency than without the choke. This therefore provides for asignificant current density reduction by widening the arms 1509′ of thedipole to a width Wda. This reduction in surface current density resultsin reduced SAR; however, the inductance decreases significantly as thewidth increases. For this reason the meander choke or inductor 1516should be increased to restore the required resonance as necessary.Another expedient is to raise the location into which the PC card ismated in the side face of the laptop computer 1500 by a distance Hct tofurther separate the hotspot from the user during use, when the laptopand PC card are resting on the users thighs. The distance Hct may betaken from the lowest point of the host device (laptop computer), suchas its bottom surface or the rest legs or points thereof.

In all, the SAR is mitigated by increasing separation distance Hdc+Hctbetween the body tissue of the operator and the dipole arms as desired,and a significant portion of this increase is attributable to anincreased Hdc in the disclosed design. Moreover, the widening of thearms decreases the surface current density and, correspondingly, theSAR.

The consideration of inductive coupling between an antenna assembly anda printed circuit board (PCB) is discussed with reference to FIGS. 16c-16 l. FIG. 16 c shows a basic inductive coupling method in which aprimary PCB loop 1607 is shown with a gap 1608 across which the signalis injected or sensed. The magnetic coupling 1610 shows the mutualcoupling to a secondary loop 1609 that in turn connects directly to anantenna system (not shown) through feed 1609.

FIG. 16 d shows a printed dipole 1613 connected to a secondary loop 1631via a feed system 1612. The mutual coupling is sensed at the gap 1611 ofthe primary loop 1632. Of note is the width W of the printed loops andtheir separation distance S, as depicted in FIG. 16 c. As long as theloop width W is substantially larger that the separation S between thetwo loops, the leakage inductance remains small relative to the mutualinductance. The mutual inductance increases as the circumference of theloops increases. It will be appreciated that this is a trade-off issuewith size and adequate mutual coupling. Capacitive tuning or matchingimproves this coupling by cancelling out any reactive or susceptivecomponents of the impedance or admittance. In some cases the separationS of the two loops 1631, 1632 may be significant—even being more thanthe width of the loops. In that case the leakage inductance becomessignificant and may exceed the mutual inductance. Such leakageinductance can be tuned out with simple matching methods. Theconsequence is to increase the Q of the circuit and thereby decrease theusable coupling bandwidth. It is generally preferred that the two loopsbe substantially aligned one atop the other. To the extent this is notthe case, the leakage inductance will increase. In some situations, theloops may be offset or side-by-side, which may satisfy applicationrequirements at a cost to bandwidth.

FIGS. 16 e-16 l show several implementations of an antenna inductivecoupling, which may be a PCB-to-FPCB pair, or a PCB-to-stamped, etchedor cut metallic antenna. It will be appreciated that the gaps in the twoloops do not have to be coincident but may be anywhere, even as far asbeing opposite to each other as seen in FIG. 16 e, wherein the dipole1616 is coupled via the feed 1615 to the upper loop 1633, theninductively coupled to the lower loop 1634 with the output gap 1614located in the opposite sense to the feed from feed system 1615. A sideview of the antenna system of FIG. 16 e is shown in FIG. 16 f, with thelower loop on the main PCB, the upper loop on the FPCB or stamped metalconnected via the feed to the dipole/radiator.

Several alternative configurations are shown in FIGS. 16 g-16 l. Theplacement of the dipole antenna clear and above the main PCB in FIG. 16g provides a more compact antenna and coupling solution, as seen in.Clearly height issues typical for dipoles above a ground plane areimportant here. A vertically (normal) disposed and may be horizontaldipole is shown in FIG. 16 h, with its coupling loop and feed system. Ahorizontal dipole with feed and coupling loop is also shown, in FIG. 16i. The antenna configuration of FIG. 16 j shows a similar system to thatin FIG. 16 g above, except that the feed system is away from the cardedge. This will affect both performance and mechanical issues. Whileantenna assemblies in FIGS. 16 g-16 j show the antenna coupling loop ontop, in FIGS. 16 k-16 l, this is reversed, with the antenna couplingloop being disposed on the opposite side or bottom of the main PCB.Inductive coupling at RF between a PCB and a SAW chip with the intentionof eliminating the wire bonds that would otherwise have been used isalso possible.

The consideration of dual band gap split duplexing and/or matching isdiscussed with reference to FIGS. 18-21. FIGS. 18 a-18 c show excitationof a gap 1816 in a waveguide structure 1815 from opposite sides. The gap1816 lies between antenna portions 1835 and 1836. Sides 1817 and 1818 ofgap 1816 are coupled to the strip lines TL1 and TL2, as seen in FIGS. 18a and 18 b. The dual excitation provides a convenient duplexing or highband low band matching opportunity. In this case the two feeds split thehigh frequency to one side and the lower frequencies to the other. It isalso possible to split multiple frequency bands to one side of theslot/gap and the other bands to the other side.

In FIGS. 18 a and 18 b, a configuration is shown in which the twotransmission lines TL1 and TL2 are connected directly to the gap 1816 byshort circuit couplings. In FIG. 18 c, the gap 1816′ is straddled by thestrip line without any direct connection to the two transmission linesTL1′ and TL2′, in an open circuit coupling configuration. The twotransmission lines TL1′ and TL2′ are joined to one another under thegap. Within a short distance or at a distance of an integral multiple ofone half of a wavelength, band pass and/or appropriate band rejectmatching impedances or filters are used in order to achieve the requiredduplexing or match splitting, as described below.

In FIG. 19 a-19 b, a combination of shunt (1927 and 1928) and series(1926 and 1929) match elements are shown applied to the gap 1816 at thegap edges to provide the appropriate band pass and band rejectconditions to achieve the desired match split or duplexing. Thedistances L1 and L2 from the gap center have a modifying effect on theband select conditions, and if it they are not made small then theyshould be considered in the matching conditions. One approach is tochoose distances L1 and L2 of integer multiples of one half of awavelength. The band reject impedances should appear as very highimpedances at the required frequencies on the associated sides. In FIG.19 b, a similar arrangement is shown, but with gap 1816′ not connectedto the two feed systems. The two feed systems instead are joined underthe gap at connecting point 1930. In this case the band rejectimpedances formed by the matches 1926′, 1927′, 1928′ and 1929′ shouldappear as very low impedances at the respective gap edges so that thecross coupling will properly function.

FIG. 20 shows some of the possible band pass and band reject circuitsthat may be employed at the gaps 1816, 1816′. For ease of understandingonly, one side illustrated; however, by extension the configuration forthe opposite side can also be inferred. For example, several matchingpass stop configurations have been shown for the matches. For the seriesmatching 1926, 1926′, any of the configurations A through D can be used.The series configuration should appear as a low impedance for the passband and as a high impedance for the band stop, while the shunt match(1927, 1927′) should supplement the series match to achieve the sameresult to the gap. Generally this means the shunt impedance will benormally high, suggesting it is only required for matching conditions.Examples of high impedance matches are shown in configurations E throughH. Configuration H has a low impedance at the series resonance, whichmust not fall either in the required band stop or band reject region butis used to achieve matching conditions. If the transmission line passesunder the gap then the band stop should have a very low impedance, aswith configurations F through H in the shunt match in the stop band anda very high impedance in the pass band. While these arrangements focuson the split at the gap into two duplexed signals, these may be feddirectly to independent Rx/Tx systems, or else recombined after matchingto establish a unified matched signal.

FIG. 21 shows one embodiment configured as described herein. The copper(or other material) region 2160 contains a BALUN 2161 with a gap 2162that is directly or inductively coupled to an antenna element (notshown). The low band signal is diverted from the gap 2162 to the rightvia a high band trap 2164 whose excess inductance in the low band iscancelled out using the series capacitor 2166. This signal is thenmatched to the desired matching conditions through the low band matchingsection 2168 and may be recombined via a similar trap arrangement 2170to the common node 2172 that is connected to the Tx/Rx RF circuit on thePCB (not shown). The trap 2164 presents a high impedance to the highband and the trap on the left side (2165) presents a high impedance tothe low band thus deflecting all the low band signal to the low bandside. Similarly the high band signal is diverted from the gap 2162 tothe left via the low band trap (2165) whose excess capacitance in thehigh band is cancelled out using the series inductor 2167. This highband signal is then matched to the desired matching conditions throughthe high band matching section 2169 and may be recombined via a similartrap arrangement 2171 to the common node 2172. Simplifications to thetraps are possible using appropriate lengths of transmission line toachieve high impedance conditions at the frequency bands as describedabove.

The above are exemplary modes of carrying out the invention and are notintended to be limiting. It will be apparent to those of ordinary skillin the art that modifications thereto can be made without departure fromthe spirit and scope of the invention as set forth in the followingclaims.

1. A diversity antenna system for use with a host device and configuredto provide isolation from radiated self-noise by the host device and tominimize interactions between antenna elements of the diversity antennasystem, the diversity antenna system comprising: a ground plane; a mainantenna coupled to the ground plane and comprising a dual-bandsymmetrical center fed dipole; and a diversity antenna coupled to theground plane and configured to operate as a top loaded monopole.
 2. Thesystem of claim 1, wherein the main antenna comprises a low bandcomponent and a high band component.
 3. The system of claim 2, whereinat least a portion of one of the low band and high band components isconfigured to be elevated relative to a surface of the system that isclosest to a user of the system such that SAR (Specific Absorption Rate)to the user is minimized.
 4. The system of claim 1, wherein the mainantenna is inductively coupled to the ground plane.
 5. The system ofclaim 4, wherein the inductive coupling is through a loop balun.
 6. Thesystem of claim 1, wherein the host device is a laptop computer.
 7. Thesystem of claim 1, wherein the host device is a portable telephone. 8.The system of claim 1, wherein the host device is a personal digitalassistant.
 9. The system of claim 1, wherein the main antenna is formedon a FPCB (flexible printed circuit board) which is configured to have athree-dimensional shape.
 10. The system of claim 1, further comprisingan RF connector oriented orthogonally to the ground plane.
 11. Adiversity antenna system for use in a wireless communication deviceremovably pluggable into a host device, the diversity antenna systemcomprising: a ground plane; a main antenna coupled to the ground planeand having at least one portion that is configured to be elevatedrelative to a surface of the wireless communication device that isclosest to a user of the system such that SAR (Specific Absorption Rate)to the user is minimized; and a diversity antenna coupled to the groundplane and configured to operate as a top loaded monopole.
 12. The systemof claim 11, wherein the main antenna is inductively coupled to theground plane.
 13. The system of claim 12, wherein the inductive couplingis through a loop balun.
 14. The system of claim 11, wherein thewireless communication device is a PCMCIA (personal computer memory cardinternational association) card.
 15. The system of claim 11, wherein thehost device is a laptop computer having a top face and having a sideface into which the wireless communication device is removablypluggable, and wherein the main antenna comprises at least one dipolehaving a dipole access that is substantially parallel to the top faceand to the side face.
 16. The system of claim 11, wherein the hostdevice is a laptop computer.
 17. The system of claim 11, wherein thehost device is a portable telephone.
 18. The system of claim 11, whereinthe host device is a personal digital assistant.
 19. The system of claim11, wherein the main antenna is formed on a FPCB (flexible printedcircuit board) which is configured to have a three-dimensional shape.20. The system of claim 11, further comprising an RF connector orientedorthogonally to the ground plane.